Solve for $x$ and $y$ using substitution. ${-2x-y = 7}$ ${y = -3x-9}$
Explanation: Since $y$ has already been solved for, substitute $-3x-9$ for $y$ in the first equation. ${-2x - }{(-3x-9)}{= 7}$ Simplify and solve for $x$ $-2x+3x + 9 = 7$ $x+9 = 7$ $x+9{-9} = 7{-9}$ ${x = -2}$ Now that you know ${x = -2}$ , plug it back into $\thinspace {y = -3x-9}\thinspace$ to find $y$ ${y = -3}{(-2)}{ - 9}$ $y = 6 - 9$ $y = -3$ You can also plug ${x = -2}$ into $\thinspace {-2x-y = 7}\thinspace$ and get the same answer for $y$ : ${-2}{(-2)}{ - y = 7}$ ${y = -3}$